Microbial communities may have short- and long-term health consequences

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Note that this observational study found that the gut microbiome of infants at 6 weeks was different based upon the mode of delivery and formula supplementation.

Be aware that the long-term implications of these differences remain unclear.

Both mode of delivery and method of feeding affected the intestinal bacterial composition of an infant, even 6 weeks after delivery, an observational study found.

After controlling for the effects of feeding method, mode of delivery (vaginal or cesarean section) was associated with stool microbiome community composition in infants (P<0.001, Q<0.001) and similar effects were observed for method of feeding (P=0.01, Q<0.001), reported Juliette C. Madan, MD, of Children's Hospital at Dartmouth in Lebanon, N.H., and colleagues.

In fact, differences in infant microbial community composition were equivalent to or slightly larger than those between feeding groups -- defined as exclusively breastfed, exclusively formula fed, and combination feeding (P=0.003), they wrote in JAMA Pediatrics.

Prior studies have examined the impact of these factors on the composition of infant microflora, but only 24 hours after delivery. Previous research had also been conducted on the effects of delivery mode and feeding method, but had not examined the effects of both of them together. Co-author Anne Hoen, PhD, of the Geisel School of Medicine at Dartmouth, said their results seem to suggest that both delivery mode and feeding method remain important even 6 weeks after delivery.

"We didn't know if those [bacterial] communities were very transient, and we're seeing it's probably a longer-term process," she said in an interview with MedPage Today. "They colonize during vaginal delivery and they stay and they really have an effect later on."

Interestingly, babies who were supplemented with formula had bacterial communities that were more similar to exclusively formula fed infants than exclusively breastfed infants (P=0.002). Babies who are born via C-section delivery are often supplemented with formula in the first few days of life, but there hadn't been research to support the idea of bacterial composition changes, even in these combination fed babies.

"We know that breastfeeding has very significant implications in terms of colonization pattern, in terms of healthy outcomes," Madan told MedPage Today. "The question is are there other things we want to do after cesarean delivery."

When examining vaginal versus C-section delivery, Madan's group found statistically significant associations in the increase in Bacteroides, which help to process complex molecules in the intestine, and Pectobacterium (P<0.001 and P=0.001, respectively), as well as a significant decrease in Staphylococcus (P=0.001), Rothia (P=0.006) and Propionibacterium (P=0.01) after adjusting for feeding method.

"If a baby is delivered by cesarean section and has a microbiome that's different than what is considered most health-promoting for its immune training, then we might be able to create or discover interventions that may be able to shape a microbiome of a baby that looks more like a healthy microbiome," she said.

The study population included 102 full-term infants from the New Hampshire Birth Cohort Study (mean gestational age 39.7 weeks). Of these, 70 were delivered vaginally and 32 by C-section. Examining feeding methods, 70 were exclusively breastfed, 26 received combination feeding, and six were exclusively formula fed.

Study limitations included the lack of generalizability as the findings are from a single U.S. cohort sampled at a single time point. The small sample size may have limited statistical power. There was also no data available on the exact proportion of breast milk-formula diet, and timing of formula supplementation was not considered.

Hoen said that the next steps would be to determine the implications of breast-fed compared with formula-fed microbiota would be later in life, and continuing to follow the cohort to watch for different outcomes such as allergies and infections.

"We need to understand what the consequences of the particular microbiome profiles are, long-term, and I think we're getting there," Hoen said. "There's still some work to be done, but once we put those two pieces of the puzzle together, you can imagine some very simple, safe low-cost interventions that would reduce some of the negative health consequences of cesarean delivery."

The study was supported by the NIH and the U.S. Environmental Protection Agency.

Madan and co-authors disclosed no relevant relationships with industry.

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